The present invention, in some embodiments thereof, relates to a wireless network architecture and method for base station utilization and, more particularly, but not exclusively, to such a method and architecture applied to wireless networks including cellular networks and including networks based on GSM and CDMA, and on WiFi, WiMAX, UMTS-LTE, Zig-Bee or UMB and to other wireless networks.
Communication systems and networks are usually characterized by a sender who wishes to transmit a message to a destination, which is located physically remote. The message can be signal, such as voice, video, images, sound, or also data, such as computer files. The communication takes place over some channel, which can be air, wire, fiber-optic line, other communication network etc. The communication starts by a signal which is sent to the channel by the sender. Because the channel usually changes the signal, and the receiver receives the signals with the usually random changes, the destination can get a different message than the one the sender wished to transmit. In order to avoid such events, the sender, or other proxy of the sender, usually uses some forms of protection against such errors. Such protection can include error correcting code (ECC), which adds redundancy to bit streams or other information forms. Such redundancy adding at the transmitter is sometimes called encoding. The destination then uses the added redundancy to select the most probable message that was sent by the sender. This processing is sometimes called decoding.
In case the destination receives inputs from multiple channels, and/or senders, where sometimes the messages from some senders and channels (e.g. multiple antennas or multiple receiving base-stations) may statistically depend on each other, the destination can use such dependency to more efficiently decode the received signals, and thus also to reduce the probability of an erroneous message reception.
Compression is a process that reduces the amount of bits used to describe certain information. Compression can be done in many ways; one of them is to use the said error correcting codes in order to obtain compression. This is because redundancy is removed in the said error correcting decoding.
Wireless communications systems and networks are frequently arranged as one or more cells or coverage areas. Each cell normally includes a base station which supports communications with mobile terminals that are located in, or enter, the communications range of the cell's base station. Transmission of signals from the base station to the mobile is often called a downlink. In contrast, transmission from the mobile to the base station is commonly referred to as an uplink. The present teaching deals with the uplink channel by way of example, and the skilled person will appreciate its application to the downlink channel.
In order to efficiently use limited communications resources, base stations may allocate different resources to different mobile nodes depending on the devices' bandwidth needs. In a multiple access system, several nodes may be transmitting data, e.g., in the form of symbols, to a base station at the same time using different frequencies/time-slots/codes. This is common in orthogonal frequency division multiple access (OFDMA) systems. In such systems, it is important that symbols from different mobile nodes arrive at the base station in a synchronized manner, e.g., so the base station can properly determine the symbol period to which a received symbol belongs and signals from different mobile nodes do not interfere with each other.
The base station uses its antennas to receive the signals that were wirelessly transmitted and then processes the received signals from the antennas to bit streams. These signals often include an ECC, in order to improve the overall system performance and reliability. The ability of the base station to efficiently process and decode the received signals, establishes both wireless network capacity, and cell size.
Both base-station and client have enough processing power to determine reliable decoding (by e.g. CRC which is embedded in every packet). In order to reduce equipment cost, the base station node can be divided into several separated parts, where the antenna can be installed elsewhere, and specifically, several receiving antennas can be connected by several possible means to the same processing/decoding unit.
When the network is wireless, the transmission between any two network nodes can be compromised by varying physical conditions, such as shadowing objects, moving reflections, and many more. One way to mitigate such effects is to use sufficient margins, so the overall performance of the wireless network is reduced. Another way is to use several antennas at both receiving and transmitting nodes, such that the physical conditions on all antennas are less susceptible to a single fading event.
Several receptions for the processing unit at the base station can be used, for example by using radio signal repeaters or relays.
Processing of the received signal from several receiving nodes can be done also by means of cooperation between several base stations (destination nodes) which can receive sufficiently high quality observations of the transmitting mobile terminal Such cooperation is done for example by forwarding received signals of helping base-stations to other base station, which jointly decodes all observations.
The forwarding base stations, referred to as the helping nodes in this document, can forward the received signal as is, or after some processing or ECC encoding, which would improve the wireless network stability and overall performance.
The way the forwarded signal travels from the helping base station to the destination base station can be through a fiber optic channel, wired line, wireless radio signal, or any other means.
The destination base station processes and/or decodes and/or decompresses the received signals from the helping base station, so that errors can be corrected and efficiency maintained, and then processes the original signal from the mobile terminal, only that now the received signal is less susceptible to the physical conditions of the channel.
Compress and forward relaying technique is a known concept which means that a helper node uses compression and error correcting coding on the received signal, for better utilization of network resources, and then forwards the compressed and encoded signal through the channel that separates the helping node and the destination node.
Known techniques for compress and forward use separated channel codes for the ECC and the compression, such as LDPC codes, Turbo codes, and convolution codes.
In many wireless networks there exist links between the base-stations (BS), which are sometimes referred to as access nodes. The links between BSs are sometimes used for performing soft-handovers or for backhaul purposes, when network infrastructure is not available at all BSs.
Soft handover is a technique to improve the communication reliability of highly mobile clients, and allow high quality of service during handover between BSs. In order to reduce the probability of disconnection, multiple BSs may be involved in maintaining the connection with a client node, and may utilize macro diversity gains for this purpose. There are different forms and protocols for implementing macro-diversity techniques, of which some are specified in cellular standards.
Some standards specify the protocols required to be supported by BSs and client nodes in order to perform soft handover in the form of macro-diversity. For example, in order to perform soft handovers between WiMAX 802.16e BSs, the client node has to allow and support a soft-handover protocol.
The related art mentions wireless network systems, such as in the following patents for example.
U.S. Pat. No. 5,276,703 to Budin et al., referred as Budin hereinbelow, discloses reference to multiple access communication systems. In particular, the disclosure relates to a local area network including at least one hub unit, one or more associated station units, and a wireless communication link between each hub unit and its associated station units. The wireless communication link includes a wireless radio frequency signal path for transferring information from each hub unit to all of its associated station units at a first frequency, f1. The communication link also includes a wireless radio frequency signal path for transmitting information from each station unit to its associated hub unit at a second frequency, f2.
Budin teaches a wireless communications link between each hub unit and its associated station units, thereby limiting each hub to communications only from the hub to the associated stations and back.
Furthermore, Budin teaches a downlink for transferring information from each hub unit to all of its associated station units, but not two hub units that communicate jointly with a single station unit.
Moreover, Budin divulges an uplink for transmitting information from each station unit to its associated hub unit, thus restricting communication from each station unit to only one single hub station.
However, according to one aspect of the present invention, it would be advantageous to provide a wireless network system having a plurality of network nodes, where each node or hub unit is configured to manage active links to mobile stations, i.e. station units. Such a wireless network system has a controller configured to control the base stations to provide at least two active links from at least two different network nodes simultaneously to a given mobile station unit in integral manner for joint signal processing of both active links.
Yet more, according to another aspect of the present invention, it would be beneficial to use error correction decoding for joint error correction, which is a novel technique operable only with joint reception. In contrast, Budin teaches the use of Trellis Modulation Encoding processing, but does not disclose, and therefore, does evidently not operate joint processing.
U.S. Pat. No. 6,470,188 to Ohtani et al., referred as Ohtani hereinbelow, teaches a method for handover, which recovers a sync state even if an out-of-sync state arises. Furthermore, Ohtani enables proper and effective quality control and informing of the out-of-sync state.    Ohtani discloses a method for handover between base stations. However, Ohtani does not consider the benefits of combining the signal information of a helper link combined with the signal information of a main link, as recited according to still another aspect of the present invention.    Furthermore, Ohtani discloses a method for handover utilizing a first and a second transmission route. The first transmission route connects a diversity handover trunk with a mobile station by way of a first base station, and therewith causes a first delay time. The second transmission route, which connects the diversity handover trunk with the mobile station by way of a second base station causes a second delay time, which is longer than the first delay time.    According to yet another aspect of the present invention, it would be advantageous to provide a joint processor that is configured such that one active communication link is the helper Link associated with another communication link, on both of which links the joint processing is performed. Thereby, joint processing is possible even when only a small amount of information is available.    The method of Ohtani also comprises a handover trigger signal involving a second base station: The handover trigger signal is communicated to the diversity handover trunk by way of a first base station. The method of Ohtani also includes receiving, by the mobile station, of the signals provided through the first and second transmission routes for combining the signals or choosing either one of the signals.    Hence, Ohtani discloses two transmission routes that limit the forwarding of information to mobile stations by way of base stations only. However, according to yet another aspect of the present invention, it would be advantageous to provide for cooperation between the base stations and to combine information.    In addition, Ohtani teaches another limitation, where the mobile stations provide a handover trigger signal, involving the second base station, to the diversity handover trunk by way of the first base station. According to an aspect of the present invention, it would be beneficial to waive the need for a handover trigger signal while still providing combination of information.    Moreover, Ohtani divulges that the combination of signals requires handover, which is another limitation, not required according to an aspect of the present invention. Yet more, Ohtani does not recite the advantages of a joint processor configured such that one active link is used to provide side information for a second active link.    In contrast to Ohtani, but according to an aspect of the present invention, the two links helping technique allow use of the joint signal processor between base stations, network nodes, and mobile stations, which is advantageous.    Ohtani further discloses changing the delay time in the first transmission route into the second delay time; transmitting, the signal directed to the mobile station, through both of the first and second transmission routes; and receiving, by the mobile station, the signals provided through the first and second transmission routes for combining the signals or choosing either of the signals. In contrast, in another aspect of the present invention, there exists combination of local beamforming with space-time coding over several base stations.
U.S. Pat. No. 6,711,409 B1 to Zavgren Jr. et. al., referred as Zavgren hereinbelow, teaches a cluster member that can forward data, or communicate through, any of its currently affiliated cluster heads. The cluster member can also determine the optimum path for delivering a particular message. Hence, Zavgren discloses relaying, which includes relaying standard packets and signaling (control) packets. However, it would be advantageous to remove the limitation of the type of information that is relayed. According to an aspect of the present invention, the type of information that is relayed is not a simple packet as with Zavgren, but is a result of joint signal processing to be relayed to another network node.
U.S. Pat. No. 6,493,759 to Passman et. al., referred as Passman hereinbelow, teaches a procedure that minimizes data loss in a communication network having member stations arranged in clusters, with each cluster having a head station. Passman thus discloses a network of member stations that communicate messages among themselves, similar to the known Internet. Hence, Passman recites homogenous networks, where a cluster head station is just another node selected out of a collection of nodes.    Furthermore, Passman discloses that depending on mobility changes of stations in a mobile network, new clusters form and cluster heads emerge as stations move around, which means reference to a mobile ad hoc clustering, where the entire network is basically wireless with mobile nodes.    In addition, Passman teaches a mobile communications station which communicates among a plurality of mobile stations in a network. Stations within the network are arranged in clusters of communication member stations, with one member station in each cluster being a head station for the cluster. Each member station communicates with the network through one or more cluster head stations. The cluster head stations communicate with other cluster head stations. The mobile station includes a transceiver that transmits signals to and receives signals from mobile stations in the network.    Hence, Passman discloses that each station in the network is a mobile station that can transmit and receive signals from all other mobile stations and that stations within the network are arranged in clusters of communication member stations. One member station in each cluster is a head station for a cluster. Each member station communicates with the network through one or more cluster head stations. Passman thus discloses a technique for clustering a general wireless network However, neither Budin, nor Budin in view of Passman, disclose, teach, or suggest the notion of a cluster of base stations for clustering a general wireless network, which is not equivalent to base station clusters. According to one aspect of the present invention, this notion is in contrast with the advantages of a way for the network operator to efficiently implement a cellular deployment, with a master base station and a slave base station, and not just a clustering technique to arrange the nodes in the network into clusters.    It is noted that neither Budin, nor Budin in view of Passman, disclose, teach, or suggest any method for handover or other similar technique. Therefore, according to an aspect of the present invention, it would be beneficial to configure the master base station to manage the active links within a cluster, to thereby provide transparent handover within the cluster.    It is yet further noted that neither Budin, nor Budin in view of Passman, disclose, teach, or suggest a technique for providing a virtual cluster, so that no external station is able to identify the operation of a cluster. Thereby, clusters may be defined by a network operator without notifying the served stations. Hence, according to an aspect of the present invention it would be of advantage to provide a cluster that is configured with a single base station address, to thereby appear externally as a single base station.    It is still further noted that neither Budin, nor Budin in view of Passman, disclose, teach, or suggest a means for a cluster of base stations to have the same address, so that the served mobile stations will be unaware of the existence of the cluster. Such means allow the use of mobile stations that are not built for being served by a cluster of base stations to be transparently served by such a cluster. According to an aspect of the present invention, it would be of advantage to provide means to cluster the base stations into slave base stations and a master base station, with the downlink being controlled by the master base station, and each base station in the cluster having a same address such that collaboration within the cluster is transparent.
U.S. Pat. No. 6,801,571 to Hyziak et al., referred as Hyziak hereinbelow, teaches data compression for wireless digital access systems. In other words, compression as recited by Hyziak is limited to the compression of user data. This is evident by the disclosure of Hyziak of V.42bis, which is a compression protocol that uses the Lempel-Ziv algorithm for compression. Such an algorithm is relevant only to non-random data, which originates from user sources, such as files, picture, and voice data. User data is lower rate data originating from users, in contrast with signals that originate from the system itself, are not compressible via a Lempel-Ziv algorithm or its equivalents, and do not depend on the specific data traffic.    It is noted that neither Budin, nor Budin in view of Hyziak, disclose, teach, or suggest any means for compression of the physically received signals, in contrast with user data. It would therefore be advantageous to provide means wherein joint signal processing comprises joint signal compression of received signals according to an aspect of the present invention. In other words, means that may receive (send) the signal in any event, to process the signal as main and helper nodes.    It is further noted that neither Budin, nor Budin in view of Hyziak, disclose, teach, or suggest any means wherein one of the base stations is a helping base station, and wherein at least one of the received signal compression and error correcting coding are jointly performed on a received signal, prior to forwarding to a destination node. However, such advantageous means are recited according to an aspect of the present invention.    It is still further noted that neither Budin, nor Budin in view of Hyziak, disclose, teach, or suggest any means wherein joint processing comprises jointly received signal compression, according to an aspect of the present invention.
The teachings of Budin in view of Passman and further in view of Zavgren, do not disclose, teach, or suggest any means wherein each base station in a cluster is configured to decode uplink information of all mobile stations which are clients of the cluster. Each base station is able to decode, and forward resulting observations directly to the access server gateway or to the master base station, the master base station being configured to decode remaining undecoded information by combining respective resulting observations. However, such advantageous means are recited according to an aspect of the present invention. In other words, these means permit the base-station to combine, by joint signal processing of information, of undecoded relayed information with the knowledge of the physical locations of the base stations to decode the transmission of the mobile stations (clients). In the disclosure of Zavgren and of Passman, every serving node provides on its own for decoding of the transmission intended thereto, and there is no relaying before decoding.    Furthermore, the teachings of Budin in view of Passman and further in view of Zavgren, do not disclose, teach, or suggest any means wherein at least some of the signals forwarded to the master base station are routed via an intermediate base station or via a backhaul channel. This means that even if taken together, Budin, Passman and Zavgren do not disclose, teach, or suggest that the relay of joint signal processing may be achieved indirectly, via another relay, as via an intermediate base-station, or via a backhaul channel, as disclosed according to an aspect of the present invention. In the teachings of Zavgren and of Passman, every serving node decodes on its own the transmission intended thereto, and thus forwarding consists of relaying only data messages. Passman recites that preferably, each mobile station can select an optimum route (e.g., a route with the “lowest cost”) to transmit messages throughout the network and Zavgren discloses a cluster member can forward data, or communicate through, any of its currently affiliated cluster heads. The cluster member can also determine the optimum path for delivering a particular message.
U.S. Pat. No. 6,477,380 to Uehara et. al., referred as Uehara hereinbelow, teaches a plurality of base stations that transmit and receive a frame to/from the mobile station. A manage station unifies the plurality of base stations. The manage station comprises an estimating circuit which estimates the location of the mobile station based upon a plurality of locations of the plurality of base stations, and a plurality of distances separating between the plurality of base stations and the mobile station. Uehara clearly recites that the location estimation is based on individual distances between each of the base station to the mobile station.    However, the teachings of Budin in view of Passman, Zavgren, and Uehara do not disclose, teach, or suggest any means wherein the system is configured with a location estimator for estimating the location of a given mobile station based on the combination of respective resulting observations. Such means are beneficial and are recited according to an aspect of the present invention, where the location estimation mechanism uses the combined information received from all the base stations, and is therefore much more accurate than the location based technique disclosed by Uehara.